[X86][SSE] Replace -cpu with equivalent -mattr for vec_cast tests

It was noticed on D47377 that these tests were being unnecessarily affected by scheduler changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333545 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed